public class Sum {
    public static double sum(){
        double ret=0;
        int flag=-1;
        for(int i=1;i<=100;i++){
            flag=-flag;
            ret=ret+(1.0/i)*flag;
        }
        return ret;
    }
    public static void main(String[] args) {
        System.out.println(sum());
    }
}
